Investigating sources and sinks for ammonia exchanges between the atmosphere and a wheat canopy following slurry application with trailing hose

(1)

HAL Id: hal-01151921

https://hal.archives-ouvertes.fr/hal-01151921

Submitted on 13 May 2015

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished or not. The documents may come from

teaching and research institutions in France or

abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est

destinée au dépôt et à la diffusion de documents

scientifiques de niveau recherche, publiés ou non,

émanant des établissements d’enseignement et de

recherche français ou étrangers, des laboratoires

publics ou privés.

Distributed under a Creative Commons Attribution - NonCommercial - NoDerivatives| 4.0

International License

Investigating sources and sinks for ammonia exchanges

between the atmosphere and a wheat canopy following

slurry application with trailing hose

Erwan Personne, F. Tardy, Sophie Génermont, Celine Decuq, Jean Christophe

Gueudet, Nicolas Mascher, Brigitte Durand, Sylvie Masson, Michel Lauransot,

Christophe Flechard, et al.

To cite this version:

Erwan Personne, F. Tardy, Sophie Génermont, Celine Decuq, Jean Christophe Gueudet, et al..

In-vestigating sources and sinks for ammonia exchanges between the atmosphere and a wheat canopy

following slurry application with trailing hose. Agricultural and Forest Meteorology, Elsevier Masson,

2015, 207, pp.11-23. �10.1016/j.agrformet.2015.03.002�. �hal-01151921�

(2)

ContentslistsavailableatScienceDirect

Agricultural

and

Forest

Meteorology

jo u rn al h om ep a g e :w w w . e l s e v i e r . c o m / l o c a t e / a g r f o r m e t

Investigating

sources

and

sinks

for

ammonia

exchanges

between

the

atmosphere

and

a

wheat

canopy

following

slurry

application

with

trailing

hose

Erwan

Personne

a,∗

_,

_Florence

_Tardy

b

_,

_Sophie

_Génermont

a

_,

_Céline

_Decuq

a

_,

_{Jean-Christophe}

Gueudet

a

_,

_Nicolas

_Mascher

a

_,

_Brigitte

_Durand

a

_,

_Sylvie

_Masson

a

_,

_Michel

_Lauransot

a

_,

Christophe

Fléchard

c

_,

_Jürgen

_Burkhardt

d

_,

_Benjamin

_Loubet

b

a_UMR₁₀₉₁_{Environnement}_et_Grandes_Cultures,_{INRA-AgroParisTech,}₇₈₈₅₀_{Thiverval-Grignon,}_France

b_UR₂₆_Systèmes_de_culture_à_base_de_bananiers,_ananas_et_plantains,_CIRAD,_Station_de_{Neufchâteau,}_Sainte_Marie,₉₇₁₃₀_{Capesterre-Belle-Eau,}

GuadeloupeFWI,France

c_UMR_1069,_SAS,_{INRA-AgroCampus}_Ouest,₆₅_Rue_de_{Saint-Brieux,}₃₅₀₄₂_Rennes,_France

d_University_of_Bonn,_Institute_of_Crop_Science_and_Resource_{Conservation,}_Plant_Nutrition_Group,_{Karlrobert-Kreiten-Str.}_13,₅₃₁₂₉_Bonn,_Germany

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received24September2014 Receivedinrevisedform 19December2014 Accepted5March2015 Keywords: Biosphere-atmosphereexchanges Compensationpoint Reactivenitrogen Model Fertilizerapplication Field Wheat

a

b

s

t

r

a

c

t

Ammoniaexchangesbetweentheatmosphereandterrestrialecosystemsarecomposedofseveral path-waysincludingexchangewiththesoil,thelitter,theplantsurfaces(cuticle)andthroughthestomata. Inthisstudy,thefateofnitrogeninthedifferentpools(soilandplant)wasanalyzedwiththeaimof determiningthesourcesandsinkofatmosphericammoniaafterslurryapplicationonawheatcanopy. Todothis,wemeasuredammoniaexchangesbetweenawinterwheatcanopyandtheatmosphere fol-lowingcattleslurryapplicationwithatrailinghose.From12Marchto8AprilinGrignonnearParis, France,theammoniaﬂuxesrangedfromanemissionpeakof54,300NH3ngm−2s−1onthedayofslurry

application(withamedianduringtheﬁrst24hof5990NH3ngm−2s−1)toadepositionﬂuxof−600NH3

ngm−2s−1(withamedianduringthelastperiodof−16NH3ngm−2s−1).Theammoniacompensation

pointswereevaluatedforapoplasm,foliarbulk,rootbulkandlitterbulktissue,aswellasforsoilsurface. Ammoniaemissionpotentialsdeﬁnedbytheratiosbetweentheconcentrationin[NH4+]and[H+]foreach

Necosystempoolwereinthesameorderofmagnitudefortheplantdecomposedinapoplasticliquid, greenleafbulktissueandcuticle,respectively,averagingat73,160and120;ingreenleafbulktissues, theemissionpotentialdecreasedgraduallyfrom230to78duringtheperiodafterslurryapplication, whileinthedeadleafbulktissuesconsideredaslitter,theemissionpotentialreachedamaximumof 50,200afterapplicationstabilizedataround20000.Thedynamicoftheemissionpotentialforrootswas similartotheammoniumconcentrationintheﬁrsttwocentimetersofthesoil,withamaximumof820 reachedtwodaysafterapplicationandaminimumof44reachedthreeweekslater.Thesurfatm-NH3

modelinterpretedtheemissionanddepositionfluxesbytestingsoilsurfaceresistance.Weconclude thatemissionofthefirstdayapplicationwasdrivenbyclimaticconditionsandammoniaconcentration atthesoilsurface,withnosurfaceresistanceandwithonlysoilsurfaceemissionpotential.Onthenext threedays,theammoniaemissionoriginatedfromthesoilsurfacewiththegrowthofadrysurfacelayer inducingsurfaceresistanceandregulatedbyslurryinfiltration.Thefollowingdaysneedamoredetailed descriptionofsoilsurfaceprocessesandtheintegrationofvegetationexchanges(stomatalandcuticle pathways),particularlyinthelastperiod,inordertoexplaintheammoniadeposition.

1. Introduction

Since the discovery of the “Haber-Bosch process” (Howard

andRees,1996),syntheticfertilizerproductionhasincreasedthe

∗ Correspondingauthor.Tel.:+33130815570;fax:+33130815563. E-mailaddress:erwan.personne@agroparistech.fr(E.Personne).

quantityofreactivenitrogen(Nr)dispersedintheenvironment, leadingtoaseriesofimpacts,labelledcollectivelyasthenitrogen cascade(Gallowayetal.,2008).Reactivenitrogenaccumulationin theenvironmentiscontributingtotheacidiﬁcationand eutrophica-tionofecosystemsandtheimpactionofairqualityandgreenhouse gasbalance(Suttonet al.,2011).One ofthemostmobile reac-tivenitrogencompoundsisammonia(NH3)anditsmobileionic

formammonium(NH4+)whichismainlyemittedbyagriculture http://dx.doi.org/10.1016/j.agrformet.2015.03.002

(3)

andespecially livestockfarming (Hertelet al.,2012;Webb and

Misselbrook,2004).Cultivatedﬁelds,especiallyafterlandspread

manure,alsoemitammonia(Sommeretal.,2003).Croplandscan howeverbeasourceorasinkofammonia,dependingonthe dif-ferencebetweentheconcentrationaboveandwithinthecanopy

(Spirig et al., 2010; Sutton et al., 1993b). The NH3 exchanges

betweentheatmosphereandterrestrialecosystemsarecomposed ofseveralpathwaysincludingexchangewiththesoil,thelitter,the plantsurfaces(cuticles)andthroughthestomata(Massadetal.,

2010;Nemitzetal.,2004;Suttonetal.,2009).Theseexchanges

alwaysincludeequilibrium processes betweenthegaseous and theaqueousphase(theHenryequilibrium),andacid-base equi-libriumeitherintheapoplast(Massadetal.,2008),inthewater layeronthecuticles(Burkhardtetal.,2009;Flechardetal.,1999)

orinthesoil(Genermontand Cellier,1997).Foreach

compart-mentinvolved,acompensationpointcanbedeﬁned(soil,litter, apoplast,andcuticle).Severalfactorsregulatestomatalﬂuxessuch asplantmetabolism,developmentstage,nitrogenstatusand cli-maticconditions(Massadetal.,2008).Factorsimpactingdeposition oncuticlesarethepresenceofliquidwateronthecuticleandthe pHofthiswater,whichisitselfdependentontheacidandbasic compoundsin thiswaterlayer(Burkhardtetal.,2009;Flechard

etal.,2011).

Because of its complexity, the NH3 exchange between

ter-restrial ecosystems and the atmosphere is still not very well parametrizedinmodels,despiterecentadvancestowardsgeneral schemes(Flechardetal.,2013;Massadetal.,2010). Comprehen-sivedatasetsincludingNH3ﬂuxesaswellasNHxcontentofeach

compartmentoftheecosystemsarerequiredtoimproveour quali-tativeunderstandingandprovideparametrizationfortheammonia exchange models.This is especially true for bi-directionalNH3

exchangesovercropswhichhaverarelybeenstudiedafter fertil-izerapplication(Bashetal.,2010;Cooteretal.,2010;Loubetetal.,

2012;Walkeretal.,2012).MeasurementsofNH3emissionsusing

up-to-datemethodsoverlargeﬁeldsarealsorequiredtovalidate NH3emissionfactorsastherearedoubtsaboutearlyworkonNH3

emissionsusingsmallﬁelds(Sintermannetal.,2012).

Inordertoproperlyunderstandtheammoniaexchangeswith theatmosphere,weanalyzedthefateofthenitrogeninthe dif-ferentpools(soilandplant)withtheobjectiveofdeterminingthe sourcesandsinkofatmosphericammoniaafterslurryapplication onawheatcanopy.Thefocuswasontheevolutionofthe concen-trationsofthedifferentformsofnitrogenforthecompartments potentiallyinvolvedbythisslurryapplication(soilandplant)andso investigatingtheoriginofthekeyexchangeswiththeatmosphere. TheexperimenttookplacenearParisduringthestem elonga-tiondevelopmentstage.ApartfromNH3ﬂuxesandconcentrations,

theNHxandNO3−contentweremeasuredinmostcompartments

atseveraldates.Chemicalcompoundsonthecuticleswerealso extractedandanalyzed.TheSurfatm-NH3model(Personneetal.,

2009)wasusedtointerprettheobservations.Finally,thelocation, magnitudeandtemporalpatternofthesourcesandsinksofNH3in

thecanopyarediscussed.

2. Materialsandmethods

2.1. Fieldsite

TheexperimentationtookplaceattheGrignonsite (NitroEu-ropeIPﬁeldsiteFR-Gri48◦51N,1◦58E)about30kmwestofParis, France,from12Marchto5April2012.Theﬁeldwasa19ha win-terwheatcrop(Triticumaestivumcv.Premio),locatedonaplateau witha gentleslopeof 1%,sownon20 October2011ata theo-reticaldensityof230seedsperm2_(measured₁₂₆_±_23)._The_soil

typewasaluvisol(loamyclay:25%clay,70%siltand 5%sand).

The mean annual precipitation and temperature were 700mm and11.5◦C,respectively.Theﬁeldwassurroundedbyother agri-culturalﬁeldsanda livestockfarmapproximately500mtothe south–west(220–240degwinddirectionsector).Twokilometres furtherinthesamedirectionwasawasteincinerationplant.During theexperimentation,themainwinddirectionswerenorth–westto south-west.

Theﬁeldwasmanagedwithamaize/winterwheat/winter bar-ley/ortriticale,mustardorPhaceliarotation.Thepreviouscropwas maizewhichwasharvestedon6September2011andstalksleft onthegroundpriortoreducedtillageandwheatseedlingon17 September2011.Thisﬁeldhasbeenmanagedwithreducedtillage since2000.

Theﬁeld wasfertilizedon13 March2012withcattleslurry usingatrailinghosesystematatargetrateof120kgNha−1.On 23March,agrowthreducer,chlormequatchloride (2-chloroethyl-trimethyl-ammoniumchloride,C5H13Cl2N)wasappliedatarateof

0.92kgha−1,whichcorrespondstoa90gNha−1and413gClha−1. Soil,plantsandslurryweresampledonthree10×10m sam-plingplotsbeforeandafterfertilization.Theseplotswerechosen withina50mradiusaroundtheﬂuxtower.Thecropwasatstem elongation(stage5onFeekes’ scale,(Zadokset al.,1974)) dur-ingtheexperiment.From29Februaryto26Marchthecropgrew from0.15mtoaround0.30mheightandtheleafareaindex(LAI) increasedfrom0.45to1.2m2_m−2_.

2.2. Micrometeorologicalmeasurements

Thethreecomponentsofthewindvelocity(u,

v

,w)and temper-ature(Tson)weremeasuredusinganultrasonicanemometer(Gill

InstrumentsLtd.,UK)at50Hz3mabovetheground.TheCO2and

H2Oconcentrationsweremeasuredat20Hzwithanopen-path

infra-redgasanalyzer(Licor,Li-7500,USA)atthesameheight.The latent(LE)andsensible(H)heatfluxesweredeterminedwiththe Eddy-covariancemethod.TheLEfluxeswerecorrectedwiththe WebbPearsonLeuningmethodforthevariationsinairdensitydue toheatandwatervapourfluxes(Aubinetetal.,2000).AnHMP-45 (Vaisala,FI)wasusedtorecordairtemperature(Ta)andrelative

humidity(RH)at 3mheight.Global(Rg)and net(Rn)radiation

weremeasuredat 3mheight,respectively,withapyranometer (CM7BAlbedometerKipp&Zonen,NL)andapyrradiometer (NR-Lite,Kipp&Zonen,NL).Thesoiltemperature(Tsoil)wasmeasured

at7 depths,withhomemadecopper-constantanthermocouples between0and20cm(0.5cm,2cm,5cm,10cm,20cm)andwith temperatureprobe(107,CampbellSci.USA)at30and90cm.The soilwatercontent(SWC)wasrecordedwithTDRprobes(CS616 timedomainreﬂectometry,CampbellSci.USA).Potentialleaf wet-ness(DH)wasmeasuredwith237wetnesssensinggrids(Campbell Sci.USA)andprecipitationswithanARG100tippingbucket rain-gauge(CampbellSci.USA).Fulldetailsofthemicrometeorological measurementscanbefoundinLoubetetal.(2011).

2.3. Ammoniaconcentrationsandﬂuxes

Ammoniaconcentrationwasintegratedduring30minat1.6, 0.75and0.4mabovegroundusingtheROSAAdevice(Robustand SensitiveAmmoniaAnalyzer,patentregistration1055253,UCPI, France). The ROSAAanalyzeris based ontrapping atmospheric ammoniainacontinuousﬂowofan0.5gL−1H2SO4acidsolution

drainedthroughthreelow-ﬂowverticalglasswetdenuders.The acidsolutionisthenanalyzedwithaconductimeterequippedwith asemi-permeablemembraneforammoniaselectivity.Adetailed descriptionoftheanalyzercanbefoundin(Loubetetal.,2012).The calibrationwasperformedwithstandardsolutionsvaryingfrom 50,100,250and500␮gNH4+kg−1to230,530,750and1000␮g

(4)

meansof352and355␮gNH4+kg−1standardsolutionsalsopassed

every2h.

TheNH3ﬂuxabovethewheatcropwasmeasuredwiththe

aero-dynamicgradientmethod(Hicksetal.,1987)detailedin(Sutton

etal.,1993a)and(Loubetetal.,2012):

FNH3=−k×u∗×

∂

CNH3

∂

[ln(z₋d)₋ H((z−d)/L)]

(1) whereu*isthefrictionvelocity(ms−1),diszeroplane

displace-ment (m), z is height above the ground surface (m), L is the Monin–Obukhovlength(m), Histhestabilitycorrectionfunction

forheatandtracegases,andkisvonKarman’sconstant(k=0.41). TheﬂuxFNH3 wasobtainedbylinearregressionbetweentheNH3

concentration(CNH3)andln(z−d)− H((z−d)/L)overthethree

measurementheightsasexplainedin(Loubetetal.,2012).By inte-gratingEq.(1),theconcentrationat1maboved,(CNH3(1m)),was

alsoestimated.

2.4. Slurryapplicationandcomposition

Thetrailinghosesystemconsistedof50hosesattachedtoa metalbaradjustedtothewheatrowsizeandsplashedslurryfrom aheightof20cm.

Todeterminethequantityof slurryintercepted bythecrop, above-groundplantsweresampledin3plots(0.0625m2₎_during

theﬁrst4hafterfertilization.Theplantsampleswereputin2L nal-genebottlesﬁlledwith1Lof0.5MKCLsolution.Nalgenebottles wereweighedbeforeandafteradditionofplantsamplesandwere shakenfor30minwithamagneticstirrer.Aftersettling,liquidwas retrieved,centrifugedandanalyzedtodeterminetotalammonia-N (TAN)concentrationwithanNH3 analyzer(FloRRia

Mechatron-ics,TheNetherlands).Plantsampleswererecovered,washedwith waterthendriedat80◦Candweighed.

Theslurry applicationvolume wasdetermined 3 timesat 5 differentrandompositionsplacedintheﬁeld,underthetrailing hosesystemduringapplicationbycollectingslurryinplasticvats (0.033075m2_).

Toanalyzetheslurrychemicalcomposition,slurrywassampled 3timesduringslurryapplication,at10h,13h,and16hT.U.in10L bucketsthenfrozenat−18◦_C_prior_to_analyzes._Three_sub-samples

weretaken fromeach bucketand analyzed at thesoilanalysis lab(LAS–INRA,Arras,France)for drymatter,pH,mineral nitro-gen,organiccarbon,totalnitrogen,NO3 andNHx.Asub-sample

(40g)wasanalyzedformoistureand another(10g)forresidual moistureforasampledriedinambientair.Asub-sampleofthe sampledriedinambientair(10g)wasusedforpHmeasurement afterbeingputin suspensioninwater. Mineralnitrogen(NO3−

andNH4+)wasanalysed,respectively,accordingtoGriess-Ilosvay

method(KeeneyandNelson,1982)andBerthelotmethod(Krom, 1980)usingspectrophotometricdeterminationonasub-sampleof 60goffreshsampleafterextractionfroma0.5molL−1KClsolution. Onalastsub-sample(50g)organiccarbonandtotalnitrogenwere analyzedaccordingtotheDumasmethod.

2.5. Soilandplantsamplingandanalysis

Plantandsoilweresampledonedaybeforefertilization,the dayoffertilizationand1,2,3,7,14and21daysaftertheslurry application.

Threesoilsamplesweretakenwithasoilaugerfromrandom locationsoneachofthethreesamplingplotsfordepths0–2cm, 2–15cmand15–30cm,andfrozenat₋₁₈◦Cpriortobeinganalyzed bythesoillabanalysis(LAS–INRA,Arras,France)withthesame methodsasforslurry.Ineachofthethreeplots,15greenleaves,

dead/yellowleaves(>50%yellow)androotsweresampledintwo rowsover1m.

Later,astheyellowleavesdisappeared,onlydeadleaveswith 100%yellow/brownbladesweresampledandconsideredaslitter. Infact,thesedeadleavesweredryandappearedtotally discon-nectedfromtheplantfunctioning,easilydetachablefromtheplant. Greenleaveswereusedforextractionofapoplasticandfoliar bulktissuesolutions,yellowanddeadleavesforfoliarbulktissue solutionextractionandrootsforrootbulktissuesolution extrac-tion.Intheextractedsolutions,pH,NH4+,NO3−andtotalNandC

weremeasured.

2.5.1. Extractionofapoplasticsolution

Amodifiedversion(Massadetal.,2009a)ofthevacuum infil-trationtechniqueof(HustedandSchjørring,1995)wasusedfor extractingapoplasticsolution.Thesub-sampleofgreenand devel-opedleaveswaswashedwithde-ionisedwater,blotteddryand weighed.Thenleaveswereputina60mLsyringewith40mLof indigocarminesolution.Thissolution,whichdoesnothavea sig-nificanteffectonpHorNH4+(Hilletal.,2001),wasinfiltratedfor

5minwith5cyclesofvacuumandpressure.Inﬁltratedleaveswere carefullydriedwithlaboratorypaperandweighed.Theapoplastic solutionwasthenobtainedbycentrifugationat2000gfor10min. Thedilutionofapoplasticsolutionbytheindigocarminesolution wasmeasuredusingaspectrophotometeratwavelength595nm (iEMSreader,Labsystems).ThepHwasmeasuredbeforethesample wasfrozeninliquidNandstoredat−18◦_C_before_further_analysis.

Thecentrifugationforceandduration weredeterminedafter cytoplasm contamination tests on wheat leaves. These con-tamination tests consisted in measuring the activity of malate dehydrogenase(MDH)in apoplastextract relativetofoliarbulk tissue extractusingaspectrophotometer atwavelength340nm

(HustedandSchjørring,1995).Thecontaminationwas1.26±0.22%

ofMDHactivityinapoplastextractsrelativetofoliarbulktissue extracts.Afterapoplastic extraction, theremaining leaveswere usedforfoliarbulktissueextraction.

2.5.2. Extractionoffoliarandrootbulktissuesolution

Sub-samplesofleavesorrootswerewashedwithde-ionised water,driedwithlaboratorypaperandgroundinliquidNusinga mortar.Asample(0.2g)ofthegroundmaterialwasputina1.5mL tubewith1mLofde-ionisedwaterandshakenfor15min.Thefoliar bulktissuesolutionwasthenextractedbycentrifugationat9000g for20min.Thesupernatantwasretrieved,andpHwasmeasured priortofreezingthesampleinliquidNandstoringat−18◦_C._The

remaininggroundmaterialwasweighed,oven-driedat80◦Cfor 48handweighedagainpriortoﬁnegrindinginaballmillmixer (Retsch,Verder,France)for3minat30pulsationspersecond.The obtainedpowderwasstoredinEppendorfcupsatambientairprior toNandCanalyses.

2.5.3. Plantanalysis

ThepHmeasurementsofapoplastic,foliarbulktissueandroot bulktissuesolutionsweremadewithapHsemi-microelectrode (InLabMicro,MettlerToledo,Udorf,Switzerland).TheNO3−

con-centrationand thetotal Nand Ccontents weremeasuredwith thesamemethodasforslurryandsoils.TheNH4+concentration

wasdeterminedusingthesameﬂowinjectionNH3analyzerasfor

slurry.

2.6. CalculationoftheNH3compensationpoint

TheNH3 compensationpointisthegaseousconcentrationat

equilibriumwithanadjacentNHxecosystempool(pool)atthesoil

surface,inthelitter,inthesub-stomatalcavityandatthecuticle surface(seeSection3.9).Itwascalculatedaccordingto(Schjørring,

(5)

1997;Schjørringetal.,1998)basedonthermodynamic equilib-riumbetweenaqueousandgaseousNH3andacid-baseequilibrium

betweenNH4+ andNH3 inthesolution(seee.g.,Personneetal.,

2009):

pool=pool×Kd×KH×exp

_H0 H+H0d R ×

1 298.15− 1 Tpool

(2) wherepoolisinmolL−1,H0HandH0darethefreeenthalpies

of volatilization (34.18kJmol−1) and acid-base dissociation (52.21kJmol−1),Ristheperfectgasconstant(8.314Jmol−1K−1), Tpooltheecosystempooltemperature(K),Kdthedissociation

con-stant for the NH4+ NH3 equilibrium at 25◦C (10−9.25molL−1),

KH the Henry constant at 25◦C (10−3.14). In Eq. (2), the ratio

pool=[NH4+]pool/[H+]pool isdimensionless,independentof

tem-peratureandrepresentstheNH3emissionpotentialofsoil,litter

orplantcompartments(root, substomatalcavity,cuticle),pools withsubscripts,l,root,stomandcut).poolwascalculatedforeach

sampleandaveragedforeachcompartment.

Thecanopyemissionpotential(z0)wasestimatedfrom

mea-suredNH3ﬂux,byinvertingEq.(2)andreplacing␹byCNH3(z0).

CNH3(z0)wasitselfestimatedbyintegrating Eq.(1) fromz0 (the

canopyroughnesslength)to1mabovethedisplacementheightd:

CNH3(z0)=CNH3(lm)+ FNH3 ku_∗ ×

ln(1/z0)− H(1/L)+ H(z0/L)

(3)

2.7. Atmosphericdepositiononthecuticles

Atmospheric depositiononthe cuticleswasanalyzed on 23 March,30Marchand5Aprilbywashingtheleaveswithde-ionised water.Threesamplingsweremadeinthemorningandthreeothers intheafternoonforeachofthesethreedays.Foreachsampling,six wheatleaveswerecollectedandputinaTeﬂonPFAbag.Thecut extremitiesofeachleafwereleftwelloutsidetheTeﬂonpocketto avoidanycontaminationwithcompoundsfrominsidetheleaves. Then2.5mL of de-ionised water wasadded in thepocket and theleafwaswashedbygentlypressurizingthebagbyhand.The leafwasthenremovedfromthepocket,anditslengthandwidth weremeasuredtodetermineitsarea.Eachsuccessive2.5mL rins-ingwaterwastransferredintoa20mLtubeleading toa 15mL sampleforeachsampling.ThepHwasmeasuredpriorto freez-ingin liquidnitrogenand storage at−18◦_C. _The_samples_were

analysedfor NO3−,PO43−,SO42−,Cl− by highperformance

liq-uidchromatography (HPLC)and forNa+ _by_inductively_coupled

plasmaatomicemissionspectrophotometry(ICP-AES).Thecuticle emissionpotentialcwascalculatedforeachsampleandaveraged.

Thenumber of wheatleavesand the quantityofde-ionised waterusedwerechosentoobtainsamplesadaptedtothe anal-ysismethods;preliminarytestswerecarriedouttoestablishthe samplingmethodwhichshowedthatmorethan80%ofNH4+ions

depositedoncuticlewereremovedaftertheﬁrstwashing(datanot shown).

2.8. InterpretationofNH3ﬂuxeswiththeSurfatm–NH3model

Tohelpinterpretthecomplexityoftheinteractionsbetweenthe ecosystemcompartments(soil,litter,stomata,cuticleandcanopy airspace),theSurfatm–NH3modelwasused.TheSurfatm–NH3isa

one-dimensionalmodel(Personneetal.,2009)calculatingtheNH3

ﬂuxinterrestrialecosystembycouplingawaterandenergy bal-ancemodelwithatwo-layerNH3resistanceanaloguemodelwhich

considerssoil,stomatalandcuticularpathways.TheSurfatm–NH3

modelwastested for agrassland canopy following cuttingand

fertilizationwithammoniumnitrate(Suttonetal.,2009),and cal-ibratedoveratriticaleﬁeldinGrignon(Loubetetal.,2012).The stomatalandsoilNH3emissionpotentialsusedinthemodelwere

interpolatedintimebetweenthosemeasuredduringthecampaign. Asourmeasurementcampaigntookplaceinthesameﬁeldasin

Loubetetal.(2012)weusedthesamemodelparametersexcept

for:

• Theattenuationcoefﬁcientforwindspeed˛u,setto2.2(instead

of4.2),toaccountforthedifferenceincanopystructure,andthe soilroughnessz0soilwasﬁxedto0.02m.

• The stomatal conductance parameters which came from

(Embersonetal.,2000)followingtheEMEPapproachforspring

wheat,onlygmaxwasmodiﬁedandﬁxedat500mmolm−2s−1.

• Thesoilsurfaceresistance(Rss), setto0thedayoftheslurry

applicationbecauseoftheliquidapplication,andthenextday ﬁxedathalfofthevaluecalculatedbytheexpressionforthevapor soil-surfaceresistance(ChoudhryandMonteith,1988)

Rss=

s×dry

ps×DH2O

(4) wheresisasoiltortuosityfactor(dimensionless),dryisthedry

soilthickness(m),psisthesoilporosity(dimensionless)andDH2O

isthemoleculardiffusionforwaterinair(m2_s−1_).

Afterthesetwospeciﬁcadaptationsforthewatersoilsurface resistanceduetotheslurryapplication,thesoilsurfaceresistance forwaterwascalculatedusingtheoriginalEq.(4).

• TheNH3 soil-surfaceresistance(RNH3soil)wasestimatedusing

twomethods:

(1)Usinganequationsimilartothatforwatersoiltransfer resis-tance(Personneetal., 2009): RNH3soil=R1=Rss×

D_H2O

D_NH3; this

approach assumesthatNH3 comesfromtheaqueousphase

whichisincorporatedinthesoilwetlayer.

• To mimicking the behavior of the cuticular resistance which decreaseswithrelativehumidity,thesoilresistancewasmade dependentonair relative humidity:RNH3soil=R2=ˇ×(100−

RH)RNH3soil=R2=ˇ×(100−RH),whereRHisrelativehumidity

at3mheight,andˇisanempiricalcoefficientwhichwas fit-tedtooptimizethecomparisonbetweenmeasuredandmodelled ammoniafluxes(ˇ=45).

Finally,inordertoevaluatetheroleofthisresistanceRNH3soil,

arunwasperformedwithRNH3soil=R0=0,inwhichthecuticular

resistancewassettoinﬁnitytosimulateemissionbythesoilonly.

3. Results

3.1. Meteorologicalconditions

Duringtheexperimentationtheairtemperaturevariedfrom −1.1◦_C _to _21.8◦_C _with _an _average _of _9.8◦_C. _Relative _humidity

rangedfrom24%to98%andaveraged70%.Theperiodwasquite dry,withsporadicraineventson14,15,17and18Marchaswellas 3and4Aprilwithamaximumof5.4mmdailyprecipitationon18 March.Thecumulatedprecipitationovertheperiodwas10.6mm. Thewindspeedaveraged2.1ms−1andvariedfrom0to6.1ms−1. Thesoilwatercontentat30cmdepthstayedalmostconstantwith anaverageof30.7%whileat5cmdepthitdecreasedfrom31.2%to 26.9%aftertheraineventon18March.Globalradiationexceeded 300Wm−2eachdayexcepton31March(Fig.1).

(6)

Table1

Cattleslurrycharacteristicsandapplicationrates.DMstandsfordrymatterandFWforfreshweight.

Slurrycharacteristics Applicationrates

n Average±standarddeviation

Applicationrate 15 92.4±37.2 Mg(FW)ha−1 Drymatter 7 59.1±9.5 g(DM)kg−1_(FW) _5.5_±_3.1 _Mg_(DM)_ha−1 OrganicC 7 406±5 gCkg−1_(DM) _2.2_±_1.3 _Mg_C_ha−1 TotalN 7 25.9±1.7 gNkg−1_(DM) ₁₄₁_±₈₉ _kg_N_ha−1 pH 7 8.3±0.3 – NO3− 7 5.7±0.6 mgNkg−1(DM) 31±21 gNha−1 NH4+ 7 20.2±1.1 gNkg−(DM) 110±68 kgNha−1

3.2. Cattleslurryapplication

Thecattleslurrywasappliedintheﬁeldwithanapplication rateof92.4Mgha−1withalargeheterogeneity(standard

devia-tion=37.2Mgha−1;Table1).Thetotalammoniacalnitrogen(TAN)

contentwas1.2gNH3–Nkg−1ofmanurewhichrepresentedaTAN

applicationrateof111kgNH3–Nha−1.ThepHoftheslurrywas

7.7±0.1.

3.3. Ammoniaconcentrationsandﬂuxes

TheatmosphericNH3concentrationat1mabovedvariedover

theperiodfrom0.8to552␮gNH3m−3(Fig.2a).Themaximal

con-centrationwasreachedintheeveningofthefertilizationday(13 March2012)withameanconcentrationduringtheﬁrst24hof 218␮gNH3m−3.Theconcentrationthendecreaseduntil19March

whenthedailymean was9␮gNH3m−3.From 20to26 March

theconcentrationrangedfromaround 20to morethan 100␮g NH3m−3andaveraged21.0␮gNH3m−3,withamarkedpeakon23

March.From28Marchtotheendofthemeasurementcampaign, ammoniaconcentrationsdidnotexceed50␮gNH3m−3.Thelast

weekofthecampaignexhibitedlowerconcentrationsaveraging 7.6_␮gNH3m−3.

Ammonia ﬂuxvaried from−2800 to54,330␮gNH3m−2s−1

with a mean of 798ng NH3m−2s−1 and a median of 31ng

NH3m−2s−1 (Fig. 2b). The main emission peak was observed

thedayofslurryspreadingwitha median5990ngNH3m−2s−1

observedovertheﬁrst24h.Thefollowingsixdaysalsoshowed largeNH3emission(median679ngNH3m−2s−1)slowly

decreas-ingtoswitchtotheﬁrstobserveddepositionﬂuxeson20March. Aone-weekperiodofalternatinghighdailyemissionsandsmall night-timedepositionwasthenobserveduntil26March,witha medianof34ngNH3m−2s−1overtheperiod.Thelastperiod(>26

March)mainlyshoweddepositionwithamedianﬂuxof−16ng NH3m−2s−1. -100 100 300 500 Rn (W m -2) 0 2 4 6 u ( m s -1) 0 1 2 3 P (mm ) 0 50 100 RH (% ) -5 5 15 25 Ta ( °C ) 26 28 30 32 11/03 13/03 15/03 17/03 19/03 21/03 23/03 25/03 27/03 29/03 31/03 02/04 04/04 06/04 08/04 SW C (% ) Date 5 cm 30 cm

Fig.1.Micrometeorologicalconditionsmeasuredatthesite.Fromtoptobottom:netradiation(Rn),windvelocityat3mheight(u),precipitation(P),relativehumidity(RH),

(7)

Table2

Totalammoniumnitrogen(TAN)applied,NH3lostbyvolatilizationandemissionfactor.

Period Wholeperiod 13/03–15/03 13/03–19/03 20/03–26/03 26/03–08/04 kgNha−1

Totalappliednitrogen(TAN) 110

CumulatedNH3ﬂux 11.1 9.1 11.5 0.02 −0.41

CumulatedNH3emission 12.9 9.1 11.5 1.06 0.35

CumulatedNH3deposition −1.8 −0.01 −0.01 −1.04 −0.76

Emissionfactor(%) 10.10% 8.20% 10.40% 0.02% −0.40%

3.4. Cumulatedvolatilizationandemissionfactor

Thecumulatedammoniaﬂuxduringtheexperimentalperiod was 11.1kg NH3−Nha−1 which was composed of 12.9kg

NH3−Nha−1 emission and −1.8kg NH3−Nha−1 deposition

(Table2).Theemissionfactorwas10.1%oftotalammoniacal

nitro-gen(TAN)applied(111kgNH3−Nha−1).Overall,8.2%ofNH3losses

occurredduringthefirstthreedaysand10.4%duringthefirstweek. Thefollowingweek(20–26/03)0.02%waslost,whileafterwards 0.4%wasdepositedbacktothecanopy.Duringthefirsttwoweeks, mostofthefluxwastowardsemission,butduringthelastthree weeks,thedepositiontermrepresentedabout1kgNha−1(Table2) andwasincludedintheemissionfactorwhichdidnotdecompose thesinkandsourcesbutquantifiedthebalance.

20000 40000 60000 F lux (ng NH 3 m -2 s -1) -1000 0 1000 11/03/2012 18/03/2012 25/03/2012 01/04/2012 08/04/2012 1000 11000 100 200 300 400 500 600 C on c en tra tion (µ g N H3 m -3) 0 25 50 75 100 11/03/2012 18/03/2012 25/03/2012 01/04/2012 08/04/2012

Fig.2.Measuredammoniaconcentrations(a)andfluxes(b)abovethewheatfield.Theverticalredlineindicatestimeoffertilization.Twoscalesareshownforconcentration andthreeforflux.Concentrationsareexpressedat1mabovethedisplacementheight.

7.5 7.6 7.7 7.8 7.9 8.0 8.1 8.2 0 20 40 60 80 100 120 140 [NH4+] [NO3-] pH 7.7 7.8 7.9 0 2 4 6 8 10 12 12/03 19/03 26/03 02/04

0 – 2 cm

15 – 30 cm

So

il

concent

rat

ion

(mg

N kg

-1

dr

y

soil

)

Date

pH

(8)

Table3

Emissionpotentials()inthedifferentpools(plant,litterandsoil)andatthecanopyscale.KnowingmeasuredNH3ﬂuxes,z0isestimatedfromEq.(3)andcisestimated

astheinterceptofthelinearﬁtbetweentheNH3ﬂuxandconcentrations.Estimatesinthesoillayers0–2cmand15–30cmarealsogiventogetherwithestimateswithinor

outsideslurrybands.

Plant Litter Soil Canopyscale

Apoplasm Cuticle Leaves Roots Litter Mixed Mixed Inslurryband Notinslurryband

0–2cm 15–30cm 0–2cm 0–2cm z0 c Whole period Average 73 120 160 340 29,000 1,700,000 24,000 – – 161,000 2200 Std.dev. 62 70 59 310 15,000 3,000,000 34,000 – – 280,000 1700 Max 110 200 230 820 50,000 5,800,000 178,000 – – 650,000 5500 Min 36 61 78 44 12,000 11,000 3000 – – 4000 300 13–19/03 Average 88 – 170 610 43,000 3,300,000 35,000 7,300,000 430,000 409,000 – Std.dev. 73 – 40 280 11,000 4,100,000 42,000 6,700,000 860,000 423,000 – 20–27/03 Average 64 114 150 170 17,000 400,000 9000 – – 33,000 3100 Std.dev. 46 – 70 40 7000 600,000 4000 – – 28,000 2400 30/03–05/04 Average 36 130 80 40 25,000 100,000 9000 – – 9000 1200 Std.dev. 60 97 80 40 25,000 100,000 – – – 9000 1000 Table4

Quantityofammonium,nitrate,phosphate,sulphate,chloride,andsodiumontheleavesmeasuredonthewheatleafsurfaces.Thepresenceofdewontheleavesduring samplingisalsoindicated.TheCl−_content_on_the_leaf_was_also_expressed_as_percentage_of_the_Cl−_dose_applied_with_the_chlormequat_chloride_on₂₃_March₍₁₁₆₅_␮mol_m−2_).

Period NH4+ NO3− PO43− SO42− Cl− Na+ Totalacids Dew(obs.) Cl−

␮molm−2_(of_leaf) _%_Appl._dose

23/03/2012 Morning 30±5.5 70±34 21±15 33±4.5 648±126 27±0.4 772±179 +++ 67% Afternoon 12±2.6 41±11 10±4.3 26±4.6 479±36 23±0.7 556±55 ø 49% 30/03/2012 Morning 23±6.9 53±6.0 5.0±1.6 33±7.5 636±145 12±0.2 727±160 ++ 65% Afternoon 13±2.7 45±10 4.4±0.6 25±13 517±188 12±0.2 591±211 ø 53% 05/04/2012 Morning 13±1.1 26±8.5 2.1±0.4 14±4.6 310±79 12±0.2 351±92 ø 32% Afternoon 13±0.6 24±1.4 1.4±0.5 12±1.4 284±95 13±0.1 321±98 ø 29% 23/03/2012 Daily 21±14 55±30 15±13 30±6.5 563±144 25±2.2 664±192 – 58% 30/03/2012 Daily 18±9.3 49±12 4.7±4.4 29±7.6 576±143 12±8.4 659±162 – 59% 05/04/2012 Daily 13±8.6 25±10 1.7±1.2 13±11 297±187 13±0.4 336±209 – 31% Average ␮molm−2_(of_leaf) ₁₇_±₁₁ ₄₃_±₂₄ _7.2_±_9.4 ₂₄_±₁₃ ₄₇₉_±₂₂₃ ₁₇_±_8.2 ₅₅₃_±₂₆₉ _– _49%

gha−1 3.1±1.5 21±10 6.9±7.8 23±10 170±68 3.8±1.7 220±96 – – mgL−1(solution) 0.15±0.06 1.0±0.4 0.3±0.3 1.1±0.4 8.1±2.8 0.2±0.1 10±4 – –

Fig.4.TemporalvariationinpH,NH4+concentrationandintheapoplast,foliarbulk,rootbulk,andlitterbulktissues(stom,green-leaves,roots,litter,respectively).

3.5. AmmoniumnitrateandpHofthetopsoil

ConcentrationsofNH4+ andNO3− aswellaspHvariedonly

inthetopsoil(0–2cm)(Fig.3).InthislayerNH4+concentration

increasedfrom0.8priortofertilizationto136mgNNH4+kg−1on

thedayoffertilization.Itmorethanhalvedthefollowingdaybefore decreasingto0.9mgNNH4+kg−1inthethirdweekofsampling.The

NO3−concentrationsincreasedfrom8.2onthedayfollowingslurry

spreadingto44.6mgN–NO3−kg−1on27March.Itthendecreased

(9)

Fig.5.Temporalvariationoftheratios([NH4+]/[H+])measuredinapoplasticsolution,foliarbulktissue,rootbulktissue,litter,soilintwolayers,oncuticlesandevaluated

atz0fromﬂuxmeasurements.Measuredrepresentmeansofthreereplicates±standarddeviation,whilez0aredailyaverages.

to7.6but,asforNH4+andNO3−concentrations,thetrendchanged

inthelastweekandthepHthenrose. 3.6. Plantpoolsofammonium,nitrateandpH

DuringtheexperimentalcampaigntheapoplasticNH4+

concen-trationofgreenleavesvariedfrom0.15to0.03␮molNH4+g−1(FW)

ofleaffreshweight,withamaximumreachedonthedayof fertil-ization(Fig.4a).TheapoplasticpHincreasedfrom5.8(12and14 March)toanaverageof6.1after15March(Fig.4b).Thefoliarbulk tissuesNH4+concentrationingreenleavesdecreasedfrom1.45to

0.62␮molNH4+g−1(FW)(Fig.4d)andinyellowleavesandlitter

variedfrom5.7to23.7␮molNH4+g−1(FW)onthesecondday

fol-lowingslurryspreading(Fig.4g).BulkpHingreenleavesremained constantduringthe12–20/03periodandaroundfertilizationat5.3 (Fig.4e).YellowleafandlitterpHwashigherandaveraged6.3later thantwodaysafternitrogenapplication(Fig.4h).Forbothgreen leavesandyellowleavesinthebulkfoliartissues,theNO3−

con-centrationvariedfrom2.3to3.7␮molNO3−g−1(FW)withoutany

visibletrend(datanotshown).

TherootbulktissueofwheatplantsshowedNH4+

concentra-tionsincreasingduringthetwodaysfollowingfertilizationtoreach 2.8_␮molNH4+g−1(FW);thisrootbulktissuecamebacktoits

ini-tiallevelaround0.6␮molNH4+g−1 (FW)(Fig.4d).Ontheother

hand,theNO3−concentrationinrootsdecreasedfrom12to2␮mol

NO3−g−1(FW),whilethepHremainedconstantandaveraged5.5

(Fig.4e).

3.7. NH3emissionpotentials

Theemissionpotentialforthestomatalpathway,stom,

aver-aged73overthewholeperiod(Fig.4c),andnosigniﬁcanttrend couldbeobservedduringtheperiod.Ingreenleavesbulktissues

greenleaves decreased gentlyfrom 235to 78 duringthe period

(Fig.4f)whileinthedeadleaves,bulktissuesconsideredaslitter

litterreachedamaximumof50,200on15Marchthenstabilizedto

around20,000duringthefollowingweeks(Fig.4i).Intheroots,bulk tissuesrootswerefoundtofollowthesameastheNH4+

concen-trationinthesoillayer0–2cm,withamaximumof820reachedon 15Marchandaminimumof44reachedthreeweekslater(Fig.4f). Ammoniaemissionpotentialsintheplantcompartments(roots, leavesandapoplast)wereallinthesameorderofmagnitude dur-ingthewholeexperimentalperiod,from60to1000(Fig.5).Onthe otherhand,theemissionpotentialfortheyellowleavesorlitter leaves(litter)wasroughlyahundredtimeslargerthanforplant,

andthesoilemissionpotential(soil)wasagainahundredtimes

largerthanlitterduringtheﬁrstweektoreach7106onthedayof

slurryapplication.Then_soildecreasedto1.1104_on₂₇_March_and

increasedagainto105_the_third_week_following_slurry_application.

Thecalculatedz0wasinbetweensoilandlitterduringthe

cam-y = 16.9x + 75.3 R² = 1.0 0 200 400 600 800 0 20 40 Cl -(µ m ol m -2) SO42-(µmol m-2) y = 2.0x + 9.1 R² = 0.8 0 20 40 60 80 0 20 40 NO 3 -(µ mo l m -2) NH4+(µmol m-2) y = 0.5x + 2.7 R² = 0.9 0 10 20 30 40 0 50 100 SO 4 2-(µ mo l m -2) NO3-(µmol m-2) y = 0.4x -8.4 R² = 0.7 0 5 10 15 20 25 0 50 100 PO 4 3-(µ m ol m -2) NO3-(µmol m-2)

(a)

(b)

(c)

(d)

Fig.6.Phosphate(a)andsulphate(b)versusnitrate.Chlorideversussulphate(c) andnitrateversusammonium(d)surface.Contentperleafsurfacemeasuredby washingwheatleavesonsixdates.Thelinearregressionline,equationsandR2_are

alsogiven.

paignandvariedfromamaximum6.5105_after_slurry_application

to4103_towards_the_end_of_March_to_increase_again_to_around₁₀4

inApril.Thecuticleammoniaemissionpotentialwasonly mea-suredoverthreedays.Itwasinthesameorderofmagnitudeasthe plantemissionpotentialsaveraging124.Finally,thecompensation pointofthecanopycwasalsoestimatedastheatmosphericNH3

concentrationwhentheﬂuxwaschangingsign.Weobtainedon averagec=21.7±6.4␮gNH3m−3duringthe20–26Marchperiod,

and8.5 _± 2.3_␮gNH3m−3duringthe28Marchto8Aprilperiod.

Basedontheaveragedairtemperatureduringtheseperiods,ac

wasestimatedat3140and1230duringthesetwoperiods(Fig.3

andTable3).

3.8. Cuticulardeposition

Theconcentrationsofthedifferentacidcompoundsand ammo-niumpresentontheleaveswerehigherinthemorningthanin theafternoonforthe23Marchand30March(Table4).Theyalso showeddifferentordersofmagnitude:PO43−wasintheorderof

1–20␮molm−2 NH4+,Na+ andSO42− wereintheorderof12to

33␮molm−2,NO3−wasintheorderof24–70␮molm−2whileCl−

wasintheorderof284–648␮molm−2.ThemuchhigherCl− con-centrationisexplainedbytheapplicationofchlormequatchloride (agrowthreducer)on23March.Indeedthetheoretical applica-tionrateofClwas413gClha−1whichamountsto1165␮molm−2. AccountingfortheLAIwhichwasmeasuredas1.2m2_m−2_on₂₆

(10)

0 25000 50000 Fl ux ( ng NH 3 m -2s -1) Measurements R0 R1 R2 -2000 2000 6000 10000 3 0 / 7 1 3 0 / 6 1 3 0 / 5 1 3 0 / 4 1 3 0 / 3 1 Fl ux ( ng NH 3 m -2s -1) -1000 1000 3000 5000 3 0 / 1 2 3 0 / 0 2 3 0 / 9 1 3 0 / 8 1 3 0 / 7 1 Fl ux ( n g N H3 m -2s -1) -600 0 600 1200 1800 21/03 22/03 23/03 24/03 25/03 26/03 Fl u x ( n g NH 3 m -2s -1) -400 -200 0 200 400 26/03 27/03 28/03 29/03 30/03 31/03 Fl ux ( ng NH 3 m -2s -1) -600 -400 -200 0 200 31/03 01/04 02/04 03/04 04/04 05/04 Fl ux ( ng NH 3 m -2s -1)

a

b

c

d

e

Fig.7. ComparisonofsimulatedandmeasuredNH3ﬂuxeswithmodelparameterisationforthesoilsurfaceresistanceRNH3soil=R0,R1andR2(seetext).Eachspeciﬁcpanel

(fromFig.7a–e)representsasequenceoffourdays;toptwopanelsareforthesamesequence.Everypanelhasitsspeciﬁcy-axisgraduationinordertofocusontheﬂux intensity.

Fig.8.SoilsurfaceresistancesforammoniaintegratingintheSurfAtmmodel,R1andR2;R1:similartosoilwaterresistancetransfer;R2:mimickingthebehaviorofthe cuticularresistanceforammonia,dependingonrelativeairhumidity.

March,theCl−leafsurfacecontentrangedfromaround60%onthe dayofapplicationandoneweeklater,anddownto30%twoweeks later.

AgoodrelationshipwasfoundbetweenSO42−andCl−which

suggestsasimilardepletionprocessforthesetwocompoundsbut witha20timeslargerconcentrationforCl−.Thenitratecontent wasalsocorrelatedtotheammoniumcontentontheleafsurface withaslopeequalto2(Fig.6).

3.9. ComparisonofthemeasuredﬂuxeswiththeSurfatm–NH3

model

The stomatal and boundary layer resistances were tuned by changing ˛u and gmax (see §2.8) in order to get a

cor-rectevapotranspiration(LE) inthemodel.Thecalibratedmodel waswellcorrelatedwiththemeasuredLE:LE(model)=1.001LE (meas)+2.06(inWm−2),withR2₌_0.89_(data_not_shown)._The

(11)

mod-elledsensibleheatﬂuxHwascomparedtothemeasuredenergy balancedefaultH(balancedefault)=Rn−LE−G(allmeasured)due tothefactthatthemeasuredenergybalancedoesnotcloseatthis

site(Loubetetal.,2011).Thesensibleheatandgroundheatﬂuxes

(Hand G)werealso satisfactorilyreproduced: H(model)=0.813 H(balancedefault)–1.97(inWm−2),R2₌_0.90_and_G(model)₌_1.02

G(meas)–2.72(inWm−2),R2₌_0.62.

ThemodeledNH3 ﬂux withthesoilemission potentialsoil

setto the measuredvalues (interpolated) reproduced wellthe firstpeakofemissionfollowingfertilizationbutoverestimatedthe measuredflux thefollowing days (Fig.7a). However,with this parametrizationthemodelednighttimefluxeswerecomparableto themeasuredvaluesthroughoutthecampaign.ThemodeledNH3

ﬂuxobtainedusingthesoiltransferresistanceR1forNH3agreed

wellwiththemeasurementsduringtheﬁrsttwodaysfollowing application(14and15/03),butnotlater.Theuseofthesoiltransfer resistanceR2witharesistancefollowingtheairrelativehumidity gaveareasonableagreementbetweenmodelledandmeasuredNH3

fluxduringtheweeksfollowingthefirstpeakofemission,and dur-ingtheperiodwithalternatingemissionsanddepositionfrom22to 26March(Fig7bandc).Thelastperiodofthesurvey(30Marchto 8April),duringwhichacontinuousdepositionfluxoccurs,isquite wellrepresentedwiththeuseofR1orR2resistances(Fig.7e).

4. Discussion

4.1. AmmoniumandpHinplantandlitterpools

Ammoniumconcentrationswerelowintheplanttissuesand apoplast(Fig.4,Table3).Theapoplasticconcentrationsandare similartowhat(Mattssonetal.,1997)and(HustedandSchjørring, 1995)reportedforBarleygrowninchambersand(Mattssonetal.,

2009;Loubetetal.,2002;Herrmannetal.,2009)forgrasslands

withnonitrogenapplication.Comparedtothereviewof(Massad

etal.,2009b),stomisroughlythreetimeslowerthanarableland

receiving150kgNha−1,wherestom∼300.

Regarding the dynamics of NH4+ concentration and , we

observednoresponsetofertilizationoftheapoplastandbulk tis-sue,which is incontradiction to(Mattsson etal.,2009; Loubet

etal.,2002;Herrmannetal.,2009).Indeed,inareview,(Massad

etal.,2010)(Fig.6), showedthatonaveragestomincreasesto

1500followinga100kgNha−1application.Therootbulktissue increasedupto1000,whilethelitterbulktissueincreasedbyfour ordersofmagnitude(40000)followingslurryapplication(Fig.4). Mattsonetal.(2009)alsofoundamuchhigherinsenescent grass-landleavesthan ingreenleavesandstems,while(Morgan and

Parton,1989)reportedanincreaseinwholeplantcompensation

pointatanthesis.Senescingleavesarenotefﬁcientsinksfor nitro-gen,thereforeanyincomingNH4+willnotbeusedasefﬁcientlyas

infast-growingleavesandmaythereforeaccumulate,whichwould explaintheobservedincreaseinNH4+insenescingleaves(Massad

etal.,2008;Massadetal.,2010).Thisissupportedbythefactthat

theinthe15–30cmsoillayer(wheretherootsarelocated)was ofthesameorderasinthelitterleaves(Fig.5).

Wheatcropsandgrasslandhavedifferentnitrogenabsorption regulationwithadifferenceintheafﬁnityforNH4andNO3.Goyal

and Huffaker (1986)reported a higher afﬁnity for nitrate than

ammoniuminwheat.Also,largeammoniumconcentrationmay inducenitrate efﬂuxes from roots as observed in cotton crops

(Aslam et al., 2001).However,wheat roots canactivelyabsorb

NH4+,andcanadaptquicklytoNH4+supply(CausinandBarneix,

1993).Theycanalsoefﬁciently absorborganicnitrogensuchas aminoacids(Giosefﬁetal.,2012).

However,when compared tothe grassland studiesreported above(Mattssonetal.,2009;Loubetetal.,2002;Herrmannetal.,

2009),amajordifferenceisthatnitrogensupplyoccurredfollowing agrasslandcut,whileherethegrowthoftheplantwas uninter-rupted.Cuttinghastwoconsequences:itinducesaremobilization ofnitrogenintheplantandhenceNH4+anditmeansthatthe

nitro-gensinkislessactiveintheplant.Inourstudythenitrogensink wasactiveandhenceNH4+whichisanintermediateintheplant

nitrogencyclewouldnotsigniﬁcantlyincrease(Massadetal.,2008,

2010a,b).

The wheat root depth did not have many roots in the top soilfraction0–2cm.Atthatstagetheshoot-to-roots(5cmdepth) biomassratioisindeedaround0.1(RecousandMachet,1999).Since theliquidmanuredidnotgreatlyinﬁltratethesoil,asdiscussedin thenextsection,untiltherainfallon17March,andsincethehigh claycontentofthesoilledtohighNH4+immobilizationontheclay

fraction,itislikelythatwheatplantsdidnotabsorbmuchNH4+

duringthatperiod.Thisisfurtherlikelybecauseoftheband appli-cationofslurrythatwouldhaveledtoadelayinrootaccessto theNsuppliedinasimilarmannerasshownby(Petersen,2005) forammonium-nitrate:theymeasureda5%m−1lossinmaximum recoveryof nitrogenand a 0.5dcm−1 increasein uptake. Since theinter-row was16cm,and theslurrybandwasroughly 5cm inwidth,wecanhypothesizea25%lossinmaximumrecoveryand a2.5daydelayforthewheattoaccessthenitrogen.Duringthat period,roughly8%oftheNwaslostbyvolatilizationleadingtoa furtherdecreaseinnitrogenaccessibletotheplant.Measurements ofthesoilNH4+concentrationoutsidetheslurrybandwasindeed6

timeslowerthanthatinthebandandpHwasalsolower,leadingto anemissionpotential()17timeshigherinthebandthanoutside

(Fig.3,Table4).

AnotherexplanationforthelowresponseofgreenleavesNH4+

toslurryapplicationisthatsoilwasalreadyrichinnitrogenand thewheatwasnotnitrogen-deﬁcient.Thetotalnitrogen measure-mentscarriedoutonthegreenleavesatthebeginningofthesurvey showa rateof5%whichisahighconcentrationforunfertilized youngwheatplants(Barthesetal.,1996;Shangguanetal.,2004). Thelowuptakeofthewheatcouldalsobeduetotheyoungageof thecropatthefertilizationdate.(Limauxetal.,1999)showedthat theamountofNuptakewaspositivelylinkedtothecropgrowth rate;inourcasethenitrogenapplicationwasearlyintheseason andthecropsmaynothavebeensufﬁcientlywell-developedto absorbalargeamountofnitrogen.Indeed,(RecousandMachet, 1999)haveshownthattheureaNuptakeofwheatwasthelowest fortheperiodofapplicationusedinthisstudy.Additionally,soil alkalinityduetotheslurrywouldtendtolowerNuptake(Wang

etal.,2012).

Wecanconcludethatwedidnotobserveanyincreaseinin thegrowingplantcompartments(excludingthesenescingleaves) following slurryapplication,which is incontradictionto previ-ous studies ongrasslands but which might be consistent with thedevelopmentalstageofthewheat(smallroots,fastgrowth), bandapplicationofslurryandgrowthofthewheatonrich culti-vatedsoil.Theobservedincreaseinsenescingleavesfollowing slurry application is consistent with existing studies and so it contributes to a pool of ammonia emission in the atmosphere (Fig.5).

4.2. AmmoniumandpHinsoilpools

Ammonium concentration and pH in the top soil fraction (0–2cm)increaseddramaticallywiththenitrogenapplicationthen decreasedquicklythedayafterandthefollowingweek.Atthesame timewenoticedanincreaseofNO3−concentration(Fig.3).ThepH

ofthetopsoil(8.1)wasveryclosetotheslurrypH(8.3)onthe dayoftheapplicationindicatingalow,shallowinfiltration,suchas hypothesizedby(Garciaetal.,2012).Thisisconfirmedbythelarge differenceobservedinsoilNH4+andbetweenshallowinfiltration

(12)

onandoutside(Table4,Figs.3and5).Shallowinﬁltrationwould haveledtoapotentialdryingoftheslurryatthesoilsurface,leading tophysicalnitrogenimmobilization,untilfurtherdecompositionor surfacerewetting.ThedecreaseinsoilNH4+concentrationresults

fromseveralprocesses:ammoniavolatilization,ammonium nitriﬁ-cation,slurryinﬁltration,NH4+transportandchemicalequilibrium

inthesoil(Genermontand Cellier,1997;Sommeret al.,2003).

ThetopsoilpHisexpectedtodecrease.ThetopsoilNH4+

con-centrationdecreasedtowardsitsinitialvalueaftertwoweeksin responsetoNH3 volatilizationandNH4+nitriﬁcationasreported

by(Genermontetal.,1997;Sommeretal.,2003).Thompsonand

Meisinger(2004) observeda longerdecayof onemonth inthe

15cmsoillayerofa soilsimilartothis study.Wecantherefore concludethatthetopsoilNH4+andNO3−concentrationsandpH

measuredfollowingslurryapplicationareintherangeofreported studies,andthattheslurrydidnotinﬁltratethesoilverydeeply, leadingtolargeNH3emissionsandaquickdecreaseofNH4+inthe

topsoil.Thesoilobtainedwashigh(Fig.5,Table3)inlinewith thelargequantityofnitrogenappliedandcomparabletovalues reportedby(Flechardetal.,2010)overgrasslandfollowingcattle slurryapplication.

4.3. Cuticulardepositionandchemicalcompoundsonthecuticle Theammoniumcontentinthesolutionsampledonthecuticle wasafactorof10lowerthanthosereportedby(Burkhardtetal., 2009)indewandguttationongrasslandleaves,whichisconsistent withthefactthatwehadtodilutethesampleforcollection,but whichalsoshowsthatNH3depositiontograsslandwasprobably

larger(Table4).However,wefoundsimilarSO42−andhigherNO3−

contentontheleaveswhencomparedto(Burkhardtetal.,2009). ThismeansthattheacidtoNH3depositionratiowasmuchhigher

inourstudythanintheirs.FinallyweﬁndaCl−contentwhichwasa factorof10largerthantheirs,whichisexplainedbytheapplication ofchlormequatchlorideon23Marchatadoseof1165_␮molm−2. Thecuticularemissionpotential(cut)wasofthesameorder

ofmagnitudeasthestom(Fig.5)suggestingperhapsacontinuity

(passivetransfer)betweentheinsideandoutsideleafsolutions.A trans-cuticulartransferratecouldbeimagined,oralateral migra-tionﬂuxinthinwaterﬁlmsalongsidestomatalguardcellsurfaces. Ammoniumdeposedonleafcuticlesshowedavariationofcontent between23Marchand04Aprilandalsobetweenthemorningand theafternoon:increasingthepresenceofwaterontheleafsurfaceis consistentwithalargerdepositionearlyintheexperimentalperiod andalsoearlyintheday(BurkhardtandEiden,1994;Burkhardt,

2009,Flechardetal.,1999).Othercompoundsmeasuredoncuticles

showedthesametemporalvariation;weassumetherearesome processesofco-depositionbetweenacidcompoundsassuggested

by(Suttonetal.,1995)and(Burkhardtetal.,2009).

4.4. InterpretationoftheammoniaﬂuxeswiththeSurfatm–NH3

model

TheaimofusingtheSurfatm–NH3modelwastoquestionthe

exchangeprocessesbytryingtoreproducethemeasuredﬂuxwith themodelconstrainedbythemeasuredstomatal,cuticularandsoil emissionpotentials.Themodelwassetupwithmeasuredstom

andsoil (0–2cm)(Fig.5), andtwo soilresistancesweretested

toaccountforthevaryingavailabilityofNH3 atthesoilsurface.

Whilethefirstpeakofemissionwaswellreproducedwithboth soil-surfaceresistances,themodelfailedtoreproducetheflux cor-rectlyduringthefollowingdaysifthesurfaceresistancewasset to0(caseR0inFig.7).Thisshowsthatammoniawasindeed avail-ableatthegroundsurfacethefirstdaybutnotafter,confirmingthe assumptionthattheslurrydidnotinfiltrateverydeeplyduringthe firstdaybutitdidsoafterwards.

Duringthenextthreedays,themodelreproducedwellthe mea-sured ﬂuxif thesoilresistancefor NH3 was parametrizedin a

similarmannerasforwatervapor(Fig.7aandb;R1case).Itcanbe supposedthatasurfaceresistancetakesplaceduetotheground surfacedrying.

However,toexplaintherepresentationofthefirsttwoweeks theassumptionwasthattheresistanceshouldbelowduringthe nightand higherduring theday,likeair relativehumidity.The Surfatmsimulatedfluxesmatchedwellwiththemeasurements overthe15/03–27/03period.R2actuallypresentsadailyvariation whichpermitsaregulationoftheammoniavaporization.It repre-sentsamixprocessbetweenmechanicalsurfaceresistancedueto thedryingprocessandNH4+/NH3availabilityintheaqueousfilm

atsoilsurface.

Concerningthelastperiod,wecansupposethe30/03–05/04 periodwaswellrepresentedbecauseoftheparticularlylow evap-oration, thestrongresistance(Fig.8)and thelow soilemission potential,favoringdepositionﬂuxes.

As in Loubet et al. (2012) a very small minimal cuticular

resistance was necessary to reproduce the largest deposition ﬂux occurring on 31 March. As previously, some processes of co-depositionbetweenacidcompoundscouldbeassumed, partic-ularlyduetothehighchlorideconcentrationontheleaveswhich seemstobepersistentontheleafsurfaces.

Theneedtoadjustsurfaceresistanceovertimetestedwiththe Surfatm–NH3simulationsincludingonlyonesoilwaterreserve;

excludingsoilphysicochemicalandbiologicalprocessessuggests thatprocessessuchasinﬁltration,nitriﬁcation,nitrateleachingor organicmatteradsorptionneedtobeevaluatedinordertobetter understandtheammoniaexchangesfollowingslurryapplications. 4.5. SourcesandsinksofNH3inthewheatcanopyandammonia

emissionfactors

As described beforewe canobserve different phases in the evolutionofNH3 ﬂux.Theﬁrstsevendaysaredominatedbyan

emissionﬂuxthenthesecondweekischaracterizedbyan alter-nationofemission anddepositionﬂuxes.Thelastperiodof the experimentationisprincipallyanammoniadepositionphase.

Thefirstphaseisexplainedbyammoniaslurryvolatilization,for thefirstdaydirectlyfromslurrysurfacedeposition,andthenthe principalsourcecomesfromthesoilsurface(Fig.7aandb)andis drivenbyinfiltration,surfacedryingandslurryphysico-chemical properties.Thenthevariationsofthesecondphasedependonthe litterandsoilsources(Fig.7bandc),andprobablydueto physic-ochemical equilibrium withsoil water and organicmatter.The stomatalpathwayisbothsourceandsink,andweassumedit reg-ulatedthecanopyammoniabalance.AsFig.5shows,soilandlitter arethemaindriversoftheammoniaexchangeinthecanopy.

The10.2%emissionfactorcalculatedoverthewhole experimen-talperiod(Table4)isconsistentwiththeresultsof(Bosch-Serra

etal.,2014),(Meadeetal.,2011),or(Martínez-Lagosetal.,2013),

whichreportammonialossesofbetween6%and18%,depending onthesoilandclimateconditions,althoughourammonialosses areinthelowrange(Sintermannetal.,2012).Severalelements areconsistenttosuggestthatnitrogenlossesinourexperimental campaignarelowerthanotherstudies.Firstofall,thetrailinghose forslurryapplicationisatechniqueinducingloweremissionthan withsplashplateapplication(Sintermannetal.,2012),then,the slurryapplicationoccursduringacoldperiodwithalowair tem-perature(averagetemperaturebelow10◦C).Thislowtemperature inducesalowcompensationpointofthenitrogenpool(plantand soil)andsoalowemissionknowingthateachincreaseof5◦Clead toadoublingoftheemissionﬂuxes(Sommeretal.,2003).Finally, themeasurementcampaigntookplaceonasoilwithlow-tillage inducingasoilstructurethatmaybemorefavorabletoinﬁltration

(13)

forslurry(noslaking).Thissoilisrelativelycarbonatedand well-drained.Thenetammoniaemissionrateisveryhighduringtheﬁrst 24hwithmorethan50%oflossesandcloseto100%after48h.

5. Conclusions

Theobjective of the articlewas toexamine theorigins and magnitude of theammonia exchangesbetween soil, plant and atmosphereafterslurryapplicationandhowitchangesdayafter day.

Weconcludethattheemissionoftheﬁrstdayapplicationis drivenbyclimaticconditionsandammoniaconcentrationdirectly obtainedatthesoilsurface,withoutsurfaceresistanceandwith onlysoilemissionpotentialaskeyparameter.Thethreenextdays, theprocessesofammoniaemissionfromsoilbehavelikesoil evap-oration,withthegrowthofadry surfacelayerinducingsurface resistanceandregulatedwithslurryinﬁltration,suggestingthat thebiologicaland physicochemical processesare minoragainst mechanicaltransferthroughthedrysurfacelayer.Thefollowing phasesneedi/amoredetaileddescriptionofthesoilsurface pro-cessesandii/theintegrationofvegetationexchanges(stomataland cuticlepathways),particularlyinthelastperiod.

Indeed,twoweeksafterslurryapplication,ourexperimentand simulationwithSurfatm–NH3 showthat thisperiod of

alterna-tionbetweenemissionanddepositionﬂuxesisdrivenbytheplant exchanges,either bythecuticle or bythe stomatalabsorption. Duringthislastperiod,itcanbeobservedthatthechloride con-centrationontheleaves,due tochemicalapplicationofgrowth reducer,continuedtobeveryhigh.Thisspeciﬁccompoundcould explaintheverylowcuticularresistanceexplainingthehighleaf deposition.

Inparallelwiththisinvestigation,concerningthetransferofthe nitrogenbetweenthedifferentpools(soilandplant)afterslurry application,theplantcompartments excludingsenescingleaves hadnoevolutionoftheiremissionpotential,probablydueto nitro-genaccessibilityand/ortotheyoungwheatplantgrowingona soilwithoutnitrogendeﬁciencyandbeingitselfwithoutnitrogen deﬁciency.

Futureworksshouldbefocusedon:

• Couplingbetweenbiologicalandphysicochemicalnitrogen pro-cessesintheﬁrstsoilcentimetersandsurfacedryinginorderto evaluatetheNavailabilityforemission.

• Understandingnitrogenuptakebythegrowingplantdepending onnitrogensoilcontentandsoilproperties.

• Physicochemicalpropertiesofthecuticleinordertobetter under-standcuticledepositionandco-deposition.

Acknowledgements

WegratefullyacknowledgeDominiqueTristandirectorofthe AgroParisTechFarmforlendinghisﬁeld.Thisstudywaspartially supportedbya grantoverseenbytheFrenchNationalResearch Agency(ANR)aspartofthe“Investmentsd’Avenir”Programme (LabExBASC;ANR-11-LABX-0034)andbyEU-FP7ECLAIRE,EU-FP7 INGOS,CASDAR“Volat’NH3,ADEME“inventairesemissions

spatial-isés”,ADEME“caissons”.

References

Aslam,M.,Travis,R.L.,Rains,D.W.,2001.Inhibitionofnetnitrateuptakeby ammoniuminpimaandacalacottonroots.CropSci.41,1130–1136.

Aubinet,M.,Grelle,A.,Ibrom,A.,Rannik,U.,Moncrieff,J.,Foken,T.,Kowalski,A.S., Martin,P.H.,Berbigier,P.,Bernhofer,C.,Clement,R.,Elbers,J.,Granier,A., Grunwald,T.,Morgenstern,K.,Pilegaard,K.,Rebmann,C.,Snijders,W., Valentini,R.,Vesala,T.,2000.Estimatesoftheannualnetcarbonandwater

exchangeofforests:theEUROFLUXmethodology.Adv.Ecol.Res.30(30), 113–175.

Barthes,L.,Deleens,E.,Bousser,A.,Hoarua,J.,Prioul,J.L.,1996.Nitrateuseand xylemexudationindetoppedwheatseedlings:anearlydiagnosisfor predictingvarietaldifferencesinnitrogenutilisation?Aust.J.PlantPhysiol.23, 33–44.

Bash,J.O.,Walker,J.T.,Katul,G.G.,Jones,M.R.,Nemitz,E.,Robarge,W.P.,2010. Estimationofin-canopyammoniasourcesandsinksinafertilizedZeamays ﬁeld.Environ.Sci.Technol.44,1683–1689,

http://dx.doi.org/10.1021/es9037269.

Bosch-SerraÀ,D.,Yagüe,M.R.,Teira-Esmatges,M.R.,2014.Ammoniaemissions fromdifferentfertilizingstrategiesinMediterraneanrainfedwintercereals. Atmos.Environ.84,204–212,

http://dx.doi.org/10.1016/j.atmosenv.2013.11.044.

Burkhardt,J.,Eiden,R.,1994.Thinwaterﬁlmsonconiferousneedles:anewdevice forthestudyofwatervapourcondensationandgaseousdepositiontoplant surfacesandparticlesamples.Atmos.Environ.28,2001–2011.

Burkhardt,J.,Flechard,C.R.,Gresens,F.,Mattsson,M.,Jongejan,P.A.C.,Erisman, J.W.,Weidinger,T.,Meszaros,R.,Nemitz,E.,Sutton,M.A.,2009.Modellingthe dynamicchemicalinteractionsofatmosphericammoniawithleafsurface wetnessinamanagedgrasslandcanopy.Biogeosciences6,67–84,

http://dx.doi.org/10.5194/bg-6-67-2009.

Causin,H.F.,Barneix,A.J.,1993.RegulationofNH4+_uptake_in_wheat_plants:_effect

ofrootammoniumconcentrationandaminoacids.PlantSoil151,211–218,

http://dx.doi.org/10.1007/BF00016286.

Choudhry,B.J.,Monteith,J.L.,1988.Afour-layermodelfortheheatbudgetof homogeneouslandsurfaces.Q.J.R.Meteorol.Soc.114,

373–398.

Cooter,E.J.,Bash,J.O.,Walker,J.T.,Jones,M.R.,Robarge,W.,2010.Estimationof NH3bi-directionalﬂuxfrommanagedagriculturalsoils.Atmos.Environ.44

(juin17),2107–2115,http://dx.doi.org/10.1016/j.atmosenv.2010.02.044. Emberson,L.D.,Simpson,D.,Tuovinen,J.P.,Ashmore,M.R.,Cambridge,H.M.,2000.

TowardaModelofOzoneDepositionandStomatalUptakeOverEurope. NorwegianMeteorologicalInstitute,Oslo.

Flechard,C.R.,Fowler,D.,Sutton,M.A.,Cape,J.N.,1999.Adynamicchemicalmodel ofbi-directionalammoniaexchangebetweensemi-naturalvegetationandthe atmosphere.Q.J.R.Meteorol.Soc.125,2611–2641.

Flechard,C.R.,Massad,R.-S.,Loubet,B.,Personne,E.,Simpson,D.,Bash,J.O.,Cooter, E.J.,Nemitz,E.,Sutton,M.A.,2013.Advancesinunderstanding,modelsand parametrizationofbiosphere-atmosphereammoniaexchange.Biogeosci. Discuss.10,5385–5497,http://dx.doi.org/10.5194/bgd-10-5385-2013. Flechard,C.R.,Nemitz,E.,Smith,R.I.,Fowler,D.,Vermeulen,A.T.,Bleeker,A.,

Erisman,J.W.,Simpson,D.,Zhang,L.,Tang,Y.S.,Sutton,M.A.,2011.Dry depositionofreactivenitrogentoEuropeanecosystems:acomparisonof inferentialmodelsacrosstheNitroEuropenetwork.Atmos.Chem.Phys.11, 2703–2728,http://dx.doi.org/10.5194/acp-11-2703-2011.

Flechard,C.R.,Spirig,C.,Neftel,A.,Ammann,C.,2010.Theannualammoniabudget offertilisedcutgrassland–part2:seasonalvariationsandcompensationpoint modeling.Biogeosciences7,537–556.

Galloway,J.N.,Townsend,A.R.,Erisman,J.W.,Bekunda,M.,Cai,Z.,Freney,J.R., Martinelli,L.A.,Seitzinger,S.P.,Sutton,M.A.,2008.Transformationofthe nitrogencycle:recenttrends,questions,andpotentialsolutions.Science320, 889–892,http://dx.doi.org/10.1126/science.1136674.

Garcia,L.,Génermont,S.,Bedos,C.,Simon,N.N.,Garnier,P.,Loubet,B.,Cellier,P., 2012.Accountingforsurfacecattleslurryinammoniavolatilizationmodels: thecaseofvolt’air.SoilSci.Soc.Am.J.76,2184,

http://dx.doi.org/10.2136/sssaj2012.0067.

Genermont,S.,Cellier,P.,1997.Amechanisticmodelforestimatingammonia volatilizationfromslurryappliedtobaresoil.Agric.For.Meteorol.88,145–167.

Giosefﬁ,E.,deNeergaard,A.,Schjoerring,J.K.,2012.Interactionsbetweenuptakeof aminoacidsandinorganicnitrogeninwheatplants.Biogeosciences9, 1509–1518,http://dx.doi.org/10.5194/bg-9-1509-2012.

Goyal,S.S.,Huffaker,R.C.,1986.TheuptakeofNO3−_,_NO2−_,_and_NH4+_by_intact

wheat(Triticumaestivum)seedlingsI.Inductionandkineticsoftransport systems.PlantPhysiol.82,1051–1056.

Herrmann,B.,Mattsson,M.,Jones,S.K.,Cellier,P.,Milford,C.,Sutton,M.A., Schjørring,J.K.,Neftel,A.,2009.Verticalstructureanddiurnalvariabilityof ammoniaexchangepotentialwithinanintensivelymanagedgrasscanopy. Biogeosciences6,15–23.

Hertel,O.,Skjøth,C.A.,Reis,S.,Bleeker,A.,Harrison,R.M.,Cape,J.N.,Fowler,D., Skiba,U.,Simpson,D.,Jickells,T.,Kulmala,M.,Gyldenkærne,S.,Sørensen,L.L., Erisman,J.W.,Sutton,M.A.,2012.Governingprocessesforreactivenitrogen compoundsintheEuropeanatmosphere.Biogeosciences9,4921–4954,

http://dx.doi.org/10.5194/bg-9-4921-2012.

Hicks,B.B.,Baldocchi,D.D.,Meyers,T.P.,Hosker,R.P.,Matt,D.R.,1987.A preliminarymultipleresistanceroutineforderivingdrydepositionvelocities frommeasuredquantities.Water.Air.SoilPollut.36,311–330.

Hill,P.W.,Raven,J.A.,Loubet,B.,Fowler,D.,Sutton,M.A.,2001.Comparisonofgas exchangeandbioassaydeterminationsoftheammoniacompensationpointin Luzulasylvatica(Huds.)gaud.PlantPhysiol.125,476–487.

Howard,J.B.,Rees,D.C.,1996.Structuralbasisofbiologicalnitrogenﬁxation.Chem. Rev.96,2965–2982.

Husted,S.,Schjørring,J.K.,1995.ApoplasticpHandammoniumconcentrationin leavesofBrassicanapusL.PlantPhysiol.109(December4),

(14)

Keeney,D.R.,Nelson,D.W.,1982.Nitrogen:Inorganicforms.InMethodsofsoil analysis,Part2.Chemicalandmicrobiologicalproperties.2nded.In:PageA.L., (Ed.)Am.Soc.Agron.9,643–698.

Krom,M.D.,1980.Spectrophotometricdeterminationofammonia:astudyofa modiﬁedBerthelotreactionusingsalicylateanddichloroisocyanurate.Analyst 105,305–316.

Limaux,F.,Recous,S.,Meynard,J.M.,Guckert,A.,1999.Relationshipbetweenrate ofcropgrowthatdateoffertiliserNapplicationandfateoffertiliserNapplied towinterwheat.PlantSoil214,49–59,

http://dx.doi.org/10.1023/A.1004629511235.

Loubet,B.,Decuq,C.,Personne,E.,Massad,R.S.,Flechard,C.,Fanucci,O.,Mascher, N.,Gueudet,J.-C.,Masson,S.,Durand,B.,Genermont,S.,Fauvel,Y.,Cellier,P., 2012.Investigatingthestomatal,cuticularandsoilammoniaﬂuxesovera growingtriticalcropunderhighacidicloads.Biogeosciences9,1537–1552,

http://dx.doi.org/10.5194/bg-9-1537-2012.

Loubet,B.,Laville,P.,Lehuger,S.,Larmanou,E.,Flechard,C.,Mascher,N., Genermont,S.,Roche,R.,Ferrara,R.M.,Stella,P.,Personne,E.,Durand,B., Decuq,C.,Flura,D.,Masson,S.,Fanucci,O.,Rampon,J.-N.,Siemens,J.,Kindler, R.,Gabrielle,B.,Schrumpf,M.,Cellier,P.,2011.Carbon,nitrogenand greenhousegasesbudgetsoverafouryearscroprotationinNorthernFrance. PlantSoil343,109–137.

Loubet,B.,Milfort,C.,Hill,P.W.,Tang,Y.S.,Cellier,P.,Sutton,M.A.,2002.Seasonal variabilityofapoplasticNH+4_and_pH_in_an_intensively_managed_grassland.

PlantSoil238,97–110.

Martínez-Lagos,J.,Salazar,F.,Alfaro,M.,Misselbrook,T.,2013.Ammonia volatilizationfollowingdairyslurryapplicationtoapermanentgrasslandona volcanicsoil.Atmos.Environ.80,226–231,

http://dx.doi.org/10.1016/j.atmosenv.2013.08.005.

Massad,R.-S.,Loubet,B.,Tuzet,A.,Autret,H.,Cellier,P.,2009a.Ammoniastomatal compensationpointofyoungoilseedrapeleavesduringdark/lightcycles undervariousnitrogennutritions.Agric.Ecosyst.Environ.133,170–182,

http://dx.doi.org/10.1016/j.agee.2009.04.020.

Massad,R.-S.,Loubet,B.,Tuzet,A.,Autret,H.,Cellier,P.,2009b.Ammoniastomatal compensationpointofyoungoilseedrapeleavesduringdark/lightcycles undervariousnitrogennutritions.Agric.Ecosyst.Environ.133,170–182,

http://dx.doi.org/10.1016/j.agee.2009.04.020.

Massad,R.S.,Loubet,B.,Tuzet,A.,Cellier,P.,2008.Relationshipbetweenammonia stomatalcompensationpointandnitrogenmetabolisminarablecrops: currentstatusofknowledgeandpotentialmodellingapproaches.Environ. Pollut.154,390–403,http://dx.doi.org/10.1016/j.envpol.2008.01.022. Massad,R.-S.,Nemitz,E.,Sutton,M.A.,2010a.Reviewandparameterisationof

bi-directionalammoniaexchangebetweenvegetationandtheatmosphere. Atmos.Chem.Phys.10(10),359–10386,

http://dx.doi.org/10.5194/acp-10-10359-2010.

Massad,R.-S.,Tuzet,A.,Loubet,B.,Perrier,A.,Cellier,P.,2010b.Modelofstomatal ammoniacompensationpoint(STAMP)inrelationtotheplantnitrogenand carbonmetabolismsandenvironmentalconditions.Ecol.Model.221,479–494,

http://dx.doi.org/10.1016/j.ecolmodel.2009.10.029.

Mattsson,M.,Hausler,R.E.,Leegood,R.C.,Lea,P.J.,Schjørring,J.K.,1997.

Leaf-atmosphereNH3exchangeinbarleymutantswithreducedactivitiesof

glutaminesynthetase.PlantPhysiol.114(August4),1307–1312.

Mattsson,M.,Herrmann,B.,David,M.,Loubet,B.,Riedo,M.,Theobald,M.R.,Sutton, M.A.,Bruhn,D.,Neftel,A.,Schjørring,J.K.,2009.Temporalvariabilityin bioassaysofthestomatalammoniacompensationpointinrelationtoplant andsoilnitrogenparametersinintensivelymanagedgrassland.Biogeosciences 6,171–179.

Meade,G.,Lalor,S.T.J.,Cabe,T.M.,2011.Anevaluationofthecombinedusageof separatedliquidpigmanureandinorganicfertilizerinnutrientprogrammes forwinterwheatproduction.Eur.J.Agron.34,62–70,

http://dx.doi.org/10.1016/j.eja.2010.10.005.

Morgan,J.,Parton,W.,1989.Characteristicsofammoniavolatilizationfromspring wheat.CropSci.29,726–731.

Nemitz,E.,Sutton,M.A.,Wyers,G.P.,Jongejan,P.A.C.,2004.Gas-particle interactionsaboveaDutchheathland:I.SurfaceexchangeﬂuxesofNH(3), SO(2),HNO(3)andHCl.Atmos.Chem.Phys.4,989–1005.

Personne,E.,Loubet,B.,Herrmann,B.,Mattsson,M.,Schjorring,J.,Nemitz,E., Sutton,M.,Cellier,P.,2009.SURFATM-NH3:amodelcombiningthesurface

energybalanceandbi-directionalexchangesofammoniaappliedattheﬁeld scale.Biogeosciences6,1371–1388.

Petersen,J.,2005.Inter-rowcropcompetitionforband-injectedammonium nitrate.PlantSoil270,83–90,

http://dx.doi.org/10.1007/s11104-004-1169-4.

Recous,S.,Machet,J.M.,1999.Short-termimmobilisationandcropuptakeof fertilisernitrogenappliedtowinterwheat:effectofdateofapplicationin spring.PlantSoil206,137–149.

Schjørring,J.K.,1997.Plant-AtmosphereAmmoniaExchange:Quantiﬁcation, PhysiologyRegulationandInteractionWithEnvironmentalFactors.R. VeterinaryandAgric.Univ.,Copenhagen,Denmark.

Schjørring,J.K.,Husted,S.,Mattsson,M.,1998.Physiologicalparameters controllingplant-atmosphereammoniaexchange.Atmos.Environ.32 (February3),491–498,http://dx.doi.org/10.1016/S1352-2310(97)00006-X. Shangguan,Z.P.,Shao,M.A.,Ren,S.J.,Zhang,L.M.,Xue,Q.,2004.Effectofnitrogen

onrootandshootrelationsandgasexchangeinwinterwheat.Bot.Bull.Acad. Sin.45,49–54.

Sintermann,J.,Neftel,A.,Ammann,C.,Haeni,C.,Hensen,A.,Loubet,B.,Flechard, C.R.,2012.Areammoniaemissionsfromﬁeld-appliedslurrysubstantially over-estimatedinEuropeanemissioninventories?Biogeosciences9, 1611–1632,http://dx.doi.org/10.5194/bg-9-1611-2012.

Sommer,S.G.,Génermont,S.,Cellier,P.,Hutchings,N.J.,Olesen,J.E.,Morvan,T., 2003.Processescontrollingammoniaemissionfromlivestockslurryinthe ﬁeld.Eur.J.Agron.19,465–486,

http://dx.doi.org/10.1016/S1161-0301(03)37-6.

Spirig,C.,Flechard,C.R.,Ammann,C.,Neftel,A.,2010.Theannualammoniabudget offertilisedcutgrassland–part1:micrometeorologicalﬂuxmeasurements andemissionsafterslurryapplication.Biogeosciences7,

521–536.

Sutton,M.A.,Fowler,D.,Moncrieff,J.B.,1993a.Theexchangeofatmospheric ammoniawithvegetatedsurfaces:I:unfertilizedvegetation.Q.J.R.Meteorol. Soc.119,1023–1045.

Sutton,M.A.,Nemitz,E.,Milford,C.,Campbell,C.,Erisman,J.W.,Hensen,A.,Cellier, P.,David,M.,Loubet,B.,Personne,E.,Schjoerring,J.K.,Mattsson,M.,Dorsey, J.R.,Gallagher,M.W.,Horvath,L.,Weidinger,T.,Meszaros,R.,Dämmgen,U., Neftel,A.,Herrmann,B.,Lehman,B.E.,Flechard,C.,Burkhardt,J.,2009. Dynamicsofammoniaexchangewithcutgrassland:synthesisofresultsand conclusionsoftheGRAMINAEintegratedexperiment.Biogeosciences6, 2907–2934,http://dx.doi.org/10.5194/bg-6-2907-2009.

Sutton,M.A.,Oenema,O.,Erisman,J.W.,Leip,A.,vanGrinsven,H.,Winiwarter,W., 2011.Toomuchofagoodthing.Nature472,159–161,

http://dx.doi.org/10.1038/472159a.

Sutton,M.A.,Pitcairn,C.E.R.,Fowler,D.,1993b.Theexchangeofammoniabetween theatmosphereandplantcommunities.Adv.Ecol.Res.24,301–393.

Sutton,M.A.,Schjorring,J.K.,Wyers,G.P.,1995.Plant-atmosphereexchangeof ammonia.Philos.Trans.R.Soc.London351,261–278.

Thompson,R.B.,Meisinger,J.J.,2004.Gaseousnitrogenlossesandammonia volatilizationmeasurementfollowinglandapplicationofcattleslurryinthe mid-AtlanticregionoftheUSA.PlantSoil266,231–246.

Walker,J.M.,Philip,S.,Martin,R.V.,Seinfeld,J.H.,2012.Simulationofnitrate, sulfate,andammoniumaerosolsovertheUnitedStates.Atmos.Chem.Phys. 12,11213–11227,http://dx.doi.org/10.5194/acp-12-11213-2012. Wang,Y.,Zhang,F.,Marschner,P.,2012.SoilpHisthemainfactorinﬂuencing

growthandrhizospherepropertiesofwheatfollowingdifferentpre-crops. PlantSoil360,271–286,http://dx.doi.org/10.1007/s11104-012-1236-1. Webb,J.,Misselbrook,T.H.,2004.Amass-ﬂowmodelofammoniaemissionsfrom

UKlivestockproduction.Atmos.Environ.38, 2163–2176.

Zadoks,J.C.,Chang,T.T.,Konzak,C.F.,1974.Adecimalcodeforthegrowthstagesof cereals.WeedRes.14,415–421,